Bootstrap Nav Disappears on Resize - html

Question

I have a Bootstrap 3 navbar. When I scale the browser window to a low resolution or access the page with my mobile I have no menu. Usually, with Bootstrap I have a collapsed navigation but it is nowhere to be found.
Here is the HTML:
<nav class="navbar navbar-default navbar-fixed-top">
<div class="container">
<div class="navbar-header">
<a class="navbar-brand" href="index.php"><img src="images/logo.png"></a>
</div>
<div id="navbar" class="navbar-collapse collapse">
<ul class="nav navbar-nav navbar-right">
<li>Home</li>
<li class="aktiv" >Advertisers</li>
<li>Publishers</li>
<li>About</li>
<li>Press</li>
</ul>
</div>
</div>
</nav>
CSS:
.navbar {
background-color: #333E48;
border: 0;
display: block!important; /* From Stack Overflow */
}
.navbar-brand > img,
.navbar-brand {
padding:0px;
margin:0;
}
.navbar-brand > img {
padding: 4px;
height: 50px;
margin: auto;
vertical-align: middle;
display: inline-block;
}
.navbar-brand,
.navbar-nav li a {
line-height: 90px;
height: 90px;
padding-top: 0px;
}
.nav-collapse.collapse {
height: auto !important; /* From Stack Overflow */
overflow: visible !important; /* From Stack Overflow */
}
I added display: block!important; to .navbar after reading Nav disappears after resize
I added height: auto !important; overflow: visible !important; to .nav-collapse.collapse after reading Twitter bootstrap responsive navigation disappears after opening and closing
Issue still persists.

Answer 1

It isn't clear in your question but your missing the toggle button to open and close the menu when your viewport is reduced, otherwise the mobile menu will always be open.
nav.navbar-default {
background: #333E48;
border: 0;
}
.navbar-default .navbar-brand > img,
.navbar-default .navbar-brand {
padding: 0px;
margin: 0;
}
.navbar-default .navbar-brand > img {
padding: 4px;
height: 50px;
margin: auto;
vertical-align: middle;
display: inline-block;
}
.navbar-default .navbar-brand,
.navbar-default .navbar-nav li a {
line-height: 90px;
height: 90px;
padding-top: 0px;
}
.navbar-default .nav-collapse.collapse {
height: auto !important;
/* From Stack Overflow */
overflow: visible !important;
/* From Stack Overflow */
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet" />
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<nav class="navbar navbar-default navbar-fixed-top">
<div class="container">
<div class="navbar-header">
<button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-collapse" aria-expanded="false"> <span class="sr-only">Toggle navigation</span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
<span class="icon-bar"></span>
</button>
<a class="navbar-brand" href="index.php">
<img src="http://placehold.it/100x50/fff/fff" />
</a>
</div>
<div class="collapse navbar-collapse" id="bs-collapse">
<ul class="nav navbar-nav navbar-right">
<li>Home
</li>
<li class="aktiv">Advertisers
</li>
<li>Publishers
</li>
<li>About
</li>
<li>Press
</li>
</ul>
</div>
</div>
</nav>

Answer 2

Just have to remove the collapse class on div#navbar
Here is a fiddle
<nav class="navbar navbar-default navbar-fixed-top">
<div class="container">
<div class="navbar-header">
<a class="navbar-brand" href="index.php"><img src="images/logo.png"></a>
</div>
<div id="navbar" class="navbar-collapse">
<ul class="nav navbar-nav navbar-right">
<li>Home</li>
<li class="aktiv" >Advertisers</li>
<li>Publishers</li>
<li>About</li>
<li>Press</li>
</ul>
</div>
</div>
</nav>
And rewrite the css for the xs view